Neptune's 'Lost' Moon Spotted for 1st Time In 20 Years (Photos)

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A tiny, mysterious moon orbiting Neptune has been spotted for the
first time in more than 20 years.

By analyzing photos taken by the Hubble Space Telescope,
scientists at the SETI Institute in Mountain View, Calif., have
caught sight of Naiad, the innermost of Neptune's
moons. The 62-mile-wide (100 kilometers) moon has remained
unseen since the cameras on NASA's Voyager 2 spacecraft
discovered it in 1989.

Scientists recently tracked Naiad across a series of eight
archival images taken by Hubble in December 2004 after using a
different technique to help cancel out Neptune's glare. Neptune
is 2 million times brighter than Naiad, so Naiad is difficult to
see from Earth, SETI officials said. [ See
photos of Neptune, the mysterious blue planet ]

"Naiad has been an elusive target ever since Voyager left the
Neptune system," SETI scientist Mark Showalter said in a
statement. Showalter announced the new findings today (Oct. 8)
during a session at the annual meeting of the American
Astronomical Society's Division for Planetary Sciences, held in
Denver.

Now that scientists have spotted the small moon again, there are
other mysteries to be solved. Naiad seems to have drifted off
course: The new observations show that the moon is now ahead of
its predicted path in orbit around
Neptune, SETI officials said.

Scientists expect that the new trajectory could have something to
do with Naiad's interaction with one of Neptune's other moons
that caused the innermost moon to speed up in its orbit. The
exact cause of the moon's new orbit won't be known until
researchers collect more data.

The images taken in 2004 also reveal something about the ring
arcs surrounding Neptune. Voyager observed four arcs during its
flyby of the system, but the newly processed images show that the
two leading arcs are absent, while the two trailing arcs haven't
changed, SETI officials said. Scientists aren't sure what is
causing this change, but the arcs have been shifting since their
discovery.

"It is always exciting to find new results in old data,"
Showalter said. "We keep discovering new ways to push the limit
of what information can be gleaned from Hubble's vast collection
of planetary images."

The same images taken by Hubble also helped Showalter and his
colleagues find another small moon orbiting Neptune — a discovery
they announced in July. The newfound moon, called
S/2004 N 1, is much smaller than Naiad, at 12 miles (20 km)
across, but it was easier to spot in the images because its orbit
takes it farther from Neptune than Naiad's orbit takes it from
the planet, SETI officials said.

S/2004 N 1 evaded Voyager 2's cameras in 1989 because of its tiny
size. During its flyby, Voyager revealed six previously unknown
moons circling Neptune. Scientists have now discovered 14 moons
in orbit around the blue planet.